Because wireline parameter and signaling requirements of telecommunication systems vary widely from country to country, manufacturers of various types of system equipments and components, such as multi-function line cards, have attempted to incorporate as many functions as possible, into what may be termed a ‘quasi-universal’ subscriber line interface circuit (SLIC), and provide the user with the ability to externally program the SLIC, so that it will conform with a given end use functionality.
Programming of such a SLIC to meet the parametric requirements of a particular installation may require the connection of one or more external components, such as resistors and/or capacitors, to respective circuits dedicated to respectively different functions. For this purpose, it has been conventional practice to provide the SLIC with separate pins for connecting each component to an associated circuit node. Not only can this result in a card configuration that has a substantially elevated pin count, but using a separate component for each circuit function connection means that there must be sufficient circuit board real estate to accommodate all the components.
As non-limiting examples, three of the more commonly employed circuit functions that entail the use of externally programmed components are: 1—noiseless or soft polarity reversal of the tip and ring terminals connected to the telephone; 2—preventing false detection (ring trip) when ringing the phone; and 3—the ability to provide a measure or estimate of the length of the wireline pair that connects the line card to the phone. Each of these functions customarily requires the connection of an external capacitor for its respective circuit and, in accordance with standard practice, described above, it has been customary to provide the SLIC with three separate pins and circuit board space for connecting three separate external capacitors with their respective signaling functions.